Superhard B4C-based composites with multifunctionality

Abstract

Materials with excellent electromagnetic interference (EMI) shielding properties are desired for various structural and functional applications. Compared to mostly investigated polymers, dense ceramics are harder and own better high temperature capability, but their EMI shielding properties and shielding mechanisms had been poorly investigated. In this study, a series of light-weight B₄C-(Ti_1-xCr_x)B₂ (x = 0, 0.1, 0.3, 0.5 and 1, BTCs) composites were reactively densified. Concomitantly with good load-bearing capabilities and high hardness, as-obtained BTCs could effectively shield EMI in X band from room temperature to 700 °C. Especially, after incorporating Cr into TiB₂, the composites exhibit an enhanced absorption loss. By intentional heat treatments to tailor dislocation densities in BTCs, the enhancements in absorption loss were identified, which were associated with the increased polarizations caused by high-density dislocations in diborides. Among these composites, B₄C-(Ti_0.9Cr_0.1)B₂ with a low density (3.3 g/cm³), high hardness (∼44 GPa) and modulus (464 GPa) exhibits the best specific EMI shielding performance (∼44 dB·cm²·g^-1), which slightly worsens at 700 °C (∼30 dB·cm²·g^-1) but still guarantees an EMI shielding efficiency of ∼99.9% alongside high absorption loss. This work not only opens a window of functional applications at high temperatures for B₄C-TiB₂ based composites, but also demonstrates element incorporating and dislocation regulation can significantly enhance EMI shielding performance of materials, especially absorption loss, providing a valuable strategy for developing high-performance ceramics with multifunctionality.